He also often played the role of backstage mediator among companies and activist investors, helping to end contentious battles between Carl C. Icahn and Dell, for example, and mentoring Daniel S. Loeb, the founder of Third Point.

Inside JPMorgan, Mr. Lee was the firm’s rainmaker and one of its longest-serving executives. He often used the firm’s enormous balance sheet to finance complicated transactions. He was also a close friend and adviser to the bank’s chief executive, Jamie Dimon, whose office was just doors away from his. When the bank was under investigation by the Justice Department and Mr. Dimon was under pressure, Mr. Lee had Tom Brady, the quarterback of the New England Patriots, call Mr. Dimon to cheer him up and tell him to “hang in there.”

He was a throwback, part of a different generation of bankers on Wall Street who were trusted advisers to corporate America based on deep relationships and insights, even as much of investment banking had become commoditized.

“As vice chairman of our company and former head of our investment bank, Jimmy made an indelible and invaluable contribution to our company, our people, our clients and our industry over his nearly 40 years of dedicated and selfless service,” Mr. Dimon said in a statement.